Suspensory ligaments of the lower limb

Introduction

The suspensory apparatus of the lower limb is one of the most critical biomechanical systems in the horse, playing a central role in weight bearing, energy storage and limb stability during locomotion. From a farriery perspective, the suspensory ligament and its associated distal support structures are profoundly influenced by hoof balance, trimming technique, shoeing strategy and ground surface interaction. Injuries to these structures are among the most common causes of chronic lameness and reduced athletic performance in both sport and leisure horses (Dyson, 2011).

A thorough understanding of suspensory anatomy, function and pathology is therefore essential for the farrier working as part of a multidisciplinary team. This essay examines the suspensory ligament of the lower limb and the navicular suspensory structures, detailing their origin, route and insertion in both the forelimb and hindlimb. Functional differences between limbs are explored alongside common injuries, diagnostic techniques, altered gait patterns and trimming and shoeing strategies aimed at mitigating strain and supporting rehabilitation.

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Overview of the suspensory ligament

The suspensory ligament forms the core component of the suspensory apparatus, which functions to prevent excessive extension of the fetlock joint during the stance phase of locomotion (Ross and Dyson, 2011). Anatomically, the suspensory ligament is derived from muscle tissue and retains a degree of elasticity and limited contractile capacity, distinguishing it from purely tendinous structures (Dyson, 2003). This ligament works in conjunction with the proximal sesamoid bones, distal sesamoidean ligaments, superficial digital flexor tendon, deep digital flexor tendon and the hoof capsule to manage high cyclical loads generated during locomotion (Clayton and Hobbs, 2017). Peak loading occurs during mid stance when the fetlock reaches maximal extension, particularly during fast work, jumping and collected movements (McGuigan and Wilson, 2003).

Suspensory ligament of the forelimb - origin, route and insertion

In the forelimb, the suspensory ligament originates from the proximopalmar surface of the third metacarpal bone and the distal row of carpal bones, including contributions from the palmar carpal ligament (Dyson, 2011). This origin is broad and firmly anchored, allowing the ligament to withstand substantial tensile forces. From its origin, the ligament descends distally along the palmar aspect of the cannon bone, positioned between the medial and lateral splint bones and closely associated with the palmar cortex of the third metacarpal bone (Budras et al., 2012).

As the ligament approaches the distal third of the metacarpus, it divides into medial and lateral branches. These branches diverge abaxially and pass around either side of the fetlock joint before inserting on the corresponding proximal sesamoid bones (Ross and Dyson, 2011). From the sesamoid bones, extensor branches arise and pass dorsally to join the common digital extensor tendon. This anatomical arrangement allows the suspensory ligament to contribute both to fetlock support and coordinated extension of the digit during breakover (Dyson, 2003).

Position of the suspensory ligament in the lower limb.

Suspensory ligament of the hindlimb - origin, route and insertion

The hindlimb suspensory ligament exhibits notable anatomical and functional differences compared with its forelimb counterpart. It originates from the proximoplantar surface of the third metatarsal bone and the distal tarsal bones, with a substantial contribution from a proximal muscular component (Budras et al., 2012). This muscle belly is particularly prominent medially and is considered to play a role in active modulation of ligament tension (Dyson, 2011).

From its origin, the hindlimb suspensory ligament runs distally along the plantar aspect of the metatarsus, again positioned between the splint bones. Proximally it is thicker and more muscular, becoming increasingly tendinous distally (Ross and Dyson, 2011). Near the fetlock, the ligament divides into medial and lateral branches which insert onto the proximal sesamoid bones. Extensor branches then pass dorsally to join the long digital extensor tendon, completing the suspensory apparatus (Budras et al., 2012).

Functional role of the suspensory ligament

The primary function of the suspensory ligament is to prevent excessive fetlock extension during weight bearing, thereby protecting the distal limb from structural failure (McGuigan and Wilson, 2003). During stance, the ligament stores elastic energy as it elongates and releases this energy during the propulsion phase, contributing to locomotor efficiency (Clayton and Hobbs, 2017).

In the forelimb, the suspensory ligament has a predominantly passive support role, reflecting the forelimb primary function in weight bearing and shock absorption (Dyson, 2011). In contrast, the hindlimb suspensory ligament contributes more actively to propulsion and engagement. The muscular component allows active contraction which assists in stabilising the fetlock during powerful hindlimb extension, particularly during jumping and collected work (Ross and Dyson, 2011). These functional differences have important implications for injury patterns and farriery management.

Navicular suspensory structures origin route and insertion

The navicular suspensory structures comprise primarily the distal sesamoidean impar ligament and the collateral sesamoidean ligaments of the navicular bone. These ligaments form a sling like support system that suspends the navicular bone between the middle and distal phalanges (Dyson and Murray, 2007).

The impar ligament originates from the distal border of the navicular bone and inserts onto the flexor surface of the distal phalanx. It follows a short direct route beneath the navicular bone and is subjected to both tensile and compressive forces during weight bearing and breakover (Dyson, 2011). The collateral sesamoidean ligaments arise from the medial and lateral borders of the navicular bone and insert onto the distal phalanx and the distal aspect of the middle phalanx. Together these ligaments stabilise the navicular bone and maintain its correct alignment relative to the deep digital flexor tendon (Murray et al., 2006).

Functional role of the navicular suspensory structures

The navicular suspensory ligaments function to stabilise the navicular bone against the forces applied by the deep digital flexor tendon as it passes over the flexor surface of the bone (Dyson and Murray, 2007). During the stance phase, the deep digital flexor tendon exerts a caudal and distal pull on the navicular bone. The impar and collateral ligaments resist this movement, preventing excessive rotation or distal displacement (Murray et al., 2006).

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These structures are particularly important during breakover, where efficient force transmission and smooth rotation of the distal limb are essential. Excessive toe length or delayed breakover significantly increases strain within the navicular suspensory apparatus, predisposing it to injury (Clayton and Hobbs, 2017).

Common injuries of the suspensory ligament

Suspensory ligament injuries may occur at the origin, within the body of the ligament, or in the branches near the sesamoid bones. Proximal suspensory desmitis is among the most common presentations, particularly in the hindlimb (Dyson, 2011). It is often associated with repetitive overload, poor hindlimb engagement and suboptimal hoof balance (Ross and Dyson, 2011).

Forelimb proximal suspensory injuries are frequently linked to long toe low heel conformation, excessive fetlock extension and work on hard ground (Dyson, 2003). Branch injuries are common in jumping and event horses where repeated maximal fetlock extension places high strain on this region. Chronic cases may develop fibrosis and loss of elasticity, reducing the energy storing capacity of the ligament (McIlwraith et al., 2014).

Common injuries of the navicular suspensory structures

Injury to the navicular suspensory structures is a major component of navicular syndrome. Lesions commonly include impar ligament desmitis and collateral sesamoidean ligament strain, often in combination with pathology of the navicular bone and deep digital flexor tendon (Dyson and Murray, 2007). These injuries predominantly affect the forelimbs and are frequently bilateral (Murray et al., 2006).

Predisposing factors include long toes, underrun heels, mediolateral imbalance and inadequate shock absorption (Clayton and Hobbs, 2017). Chronic overload leads to microdamage, inflammation and degenerative change within the ligament fibres, resulting in persistent lameness if not appropriately managed (Dyson, 2011).

Differences between forelimb and hindlimb injuries

Forelimb suspensory and navicular injuries often present with more overt lameness due to the greater weight bearing demands placed on the forelimbs (Dyson, 2003). Horses may demonstrate shortened stride length, reduced heel first landing and increased concussion. Hindlimb suspensory injuries, by contrast, frequently present as poor performance, reduced impulsion or resistance to engagement rather than obvious lameness (Ross and Dyson, 2011).

The muscular component of the hindlimb suspensory ligament contributes to prolonged recovery times and a higher risk of recurrence, emphasising the importance of precise farriery intervention (Dyson, 2011).

Diagnostic techniques

Diagnosis of suspensory and navicular suspensory injuries relies on a combination of clinical examination, diagnostic analgesia and imaging (Dyson, 2011). Palpation may reveal pain or enlargement, while flexion tests may exacerbate lameness but lack specificity.

Ultrasonography is widely used to assess ligament fibre pattern, cross sectional area and echogenicity and is invaluable for monitoring healing (Ross and Dyson, 2011). Magnetic resonance imaging provides superior visualisation of soft tissue and osseous pathology within the foot and is considered the gold standard for diagnosing navicular suspensory injuries (Murray et al., 2006). Radiography remains important for assessing hoof balance and associated bony change.

MRI showing a medial suspensory branch strain.

Altered gait patterns associated with suspensory injury

Forelimb suspensory injuries often result in reduced fetlock descent during stance as a

protective adaptation. Horses may land toe first and shorten the cranial phase of the stride, leading to secondary hoof capsule distortion over time (Clayton and Hobbs, 2017).

Hindlimb injuries typically result in reduced propulsion, shortened stride length and difficulty maintaining engagement. Subtle deviations such as plaiting or lateral deviation of the limb may be observed as the horse attempts to reduce load on the injured structure (Dyson, 2011).

Principles of trimming in suspensory ligament rehabilitation

Trimming plays a central role in managing suspensory injuries by influencing limb alignment and reducing peak ligament strain. Shortening excessive toe length reduces the lever arm and decreases fetlock extension forces (Clayton and Hobbs, 2017).

In the forelimb, promoting a consistent heel first landing and adequate palmar support is critical. Mediolateral balance must be carefully maintained to prevent uneven loading of the suspensory branches (Ross and Dyson, 2011). In the hindlimb, trimming should aim to improve plantar support and symmetry while facilitating timely breakover to reduce proximal suspensory strain (Dyson, 2011).

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Shoeing options for suspensory ligament injuries

Shoeing strategies should be tailored to the individual horse, limb affected and stage of injury. Rolled or rockered toes can reduce breakover resistance and fetlock extension (Clayton and Hobbs, 2017). Wide web shoes may help distribute load across a greater surface area and improve stability during rehabilitation.

In hindlimb cases, careful heel support may reduce excessive plantar strain, but over elevation must be avoided to prevent secondary issues higher up the limb (Ross and Dyson, 2011).

Shoeing considerations for navicular suspensory injuries

Management of navicular suspensory injuries centres on reducing tension in the deep

digital flexor tendon and improving breakover efficiency. Shortening the toe and optimising hoof balance are fundamental principles (Dyson and Murray, 2007).

Gradual heel support achieved through trimming and appropriate shoe selection can reduce strain on the impar ligament, while excessive wedging should be avoided due to its potential to increase proximal limb loading (Clayton and Hobbs, 2017).

Conclusion

The suspensory ligament and navicular suspensory structures are fundamental to equine locomotion and athletic performance. Their complex anatomy and high mechanical demands render them vulnerable to injury, particularly when hoof balance and limb biomechanics are compromised. For the farrier, an in depth understanding of anatomy, function and pathology in both forelimbs and hindlimbs is essential. Through informed trimming and shoeing, close collaboration with veterinary professionals and ongoing reassessment, the farrier plays a pivotal role in both the prevention and rehabilitation of suspensory related injuries, supporting long term soundness and performance.

References

Budras, K.D., Sack, W.O. and Rock, S. (2012) Anatomy of the Horse. 6th edn. Hannover: Schlütersche.

Clayton, H.M. and Hobbs, S.J. (2017) ‘The role of biomechanical analysis in equine locomotion research’, Equine Veterinary Journal, 49(5), pp. 560–568.

Dyson, S.J. (2003) ‘Proximal suspensory desmitis in the horse’, Equine Veterinary Education, 15(2), pp. 89–99.

Dyson, S.J. (2011) Diagnosis and Management of Lameness in the Horse. 2nd edn. St Louis: Elsevier Saunders.

Dyson, S.J. and Murray, R. (2007) ‘Navicular disease and its management’, Equine Veterinary Education, 19(7), pp. 373–381.

McGuigan, M.P. and Wilson, A.M. (2003) ‘The effect of gait and digital flexor muscle activation on limb compliance in the horse’, Journal of Experimental Biology, 206(8), pp. 1325–1336.

McIlwraith, C.W., Frisbie, D.D. and Kawcak, C.E. (2014) Joint Disease in the Horse. 2nd edn. Philadelphia: Elsevier.

Murray, R.C., Schramme, M.C., Dyson, S.J. and Branch, M.V. (2006) ‘Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain’, Equine Veterinary Journal, 38(2), pp. 104–113.

Ross, M.W. and Dyson, S.J. (2011) Diagnosis and Management of Lameness in the Horse. 2nd edn. St Louis: Elsevier Saunders.